Britain and the US rounded on the Syrian government yesterday, recalling embassy staff and issuing stern warnings to the regime to end its fierce crackdown on dissent. The move came as a renewed assault on the opposition stronghold of Homs was reported to have left dozens more people dead.

The surge in violence prompted the US to close its embassy in Damascus and pull all American diplomats out of the country. William Hague, the British Foreign Secretary, said he had summoned the Syrian ambassador in London to express his "abhorrence at violence that is utterly unacceptable to the civilised world". Mr Hague also said in a statement to the House of Commons that he was recalling the British ambassador in Damascus for consultations, after the breakdown at the UN on Saturday of a united diplomatic front.

The double veto by China and Russia of the Arab League-backed plan calling on all sides to halt violence and for a peaceful transition of power has left Arab and Western nations scratching their heads over the best way to proceed. The US has called for a "Friends of Syria" group to be set up to help unite the opposition groups and provide more humanitarian aid, but Western leaders remain adamant that military action is not on the table.

"Not every situation is going to allow for the kind of military solution we saw with Libya," said Barack Obama.

China's foreign ministry spokesman, Liu Weimin, yesterday defended its use of the veto, saying the draft resolution went to the vote before the text had been agreed by all nations, while Russia's Foreign Minister, Sergei Lavrov, is due in Syria today for talks with President Bashar al-Assad. He will be arriving during some of the fiercest fighting since protests against the authoritarian regime erupted last March. The UN says more than 5,600 people have been killed during the demonstrations.

Al-Jazeera television shows footage taken by activists showing explosions and plumes of smoke rising from what they said were neighbourhoods of Homs. In central Damascus, it was business as usual with roads snarled with traffic and a light security presence. But some reports suggested that just 20 miles outside the capital there was fierce shelling of the mountain town of Zabadani, which came under effective rebel control in January.

While Zabadani is one of a handful of Damascus neighbourhoods which have seen outbursts of unrest, Homs –- about 100 miles north of the capital – appears to have become the centre of armed resistance. On Friday night and in the early hours of Saturday, sustained shelling of the city is reported to have killed up to 200 people.